Northern person who could be picky is more into The Order (6)
I believe the answer is:
neater
'could be picky is more into the order' is the definition.
I can't tell whether this definition defines the answer.
'northern person' is the wordplay.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'person' becomes 'eater' (eater is a kind of person).
'n'+'eater'='NEATER'
'who' is the link.
Can you help me to learn more?
(Other definitions for neater that I've seen before include "Less messy" , "Tidier" , "More tidy and uncluttered" , "Less untidy" , "approaching apple-pie order" .)